my %values = (
	foo => 1,
	bar => 2,
	baz => 3,
);

my %rev_values = do_something(\%values);

sub do_something {
	my $h_ref = shift;
	my %backwards;
	foreach my $key (keys %$h_ref) {
		print "$key => ", $h_ref->{$key}, "\n";
		$backwards{$h_ref->{$key}} = $key;
	}
	return \%backwards;
}